The road to the ElectroWeak

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The road to the ElectroWeak
Symmetry Breaking

14
th

-

15
th

February 2012

Seminar at DESY



S.Bolognesi (Johns Hopkins University)

Outline



Status:
CMS
results

in a
nutshell, focusing on
high mass H
-
>VV



move to
larger
mass (>600 GeV beyond SM)



improve
sensitivity to

smaller
xsec

-
> Vector Boson Fusion



The final arbiter:
VV scattering

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

2



The Higgs boson and the
ElectroWeak Symmetry Breaking (EWSB)



control of V+jets background



jet merging



signal characterization (angular analysis)



What’s next ?



control of V
V

background

Why we need the Higgs

The Higgs boson provides

1) an EXPLICATION of the
W,Z mass (ie EWSB)

2) a DESCRIPTION of the
fermions masses



1
i
s really fundamental to make the SM “working”
(next slides)
… even if not less arbitrary!



2
i
s just another way of formulating the same question:

why the fermions have those particular masses?

why the fermions have those particular Higgs couplings?

(SM works well without 2: just the
fermio
-
phobic Higgs
)

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

3


EWSB and the W, Z mass

Gauge invariance

SU(2)

U(1)
EM


complex scalar
doublet of
SU(2)

scalar potential (
l
㸰Ⱐ

㰰

with minimum
(
=

empty state)

at

SU(
2
)

3

Goldstone

bosons

w
i

1

physical

scalar
field

(
v

=
empty

expectation

value
)

generic

Gauge

Gauge unitario

4

Gauge

fields

combined

into

known

vector

bosons
:
W
,
Z

with

mass,
photon

massless

1

physical

scalar
field

-
>
Higgs

4

Gauge

fields

W
i

,
B


U(1)

or

×

February 2012, DESY seminar

4

V

V

Higgs and
unitarity

in VBF

VBF is the smoking gun of the EWSB !

Same behavior for all VV amplitudes

(
s

channel

only
)

(
t

channel

only
)

(
t

and
u

channels
)

canale

S

canale T


QGC

V

V

V

VV
-
> VV

Vector Boson Fusion (VBF)

W,Z mass (
-
> longitudinal degrees of freedom) arise from the Higgs mechanism:

without Higgs, W
+
L
W
-
L
-
>W
+
L
W
-
L

would break
unitarity


V

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

5

VBF and VV scattering



VV scattering spectrum
s
(VV
-
>VV)
vs

M(VV)



Whatever we will see or not see at low mass (<2
×
m
W
), the EWSB mechanism
must be probed in the VV final state



search for possible
resonances
in VBF



measurement of
VV scattering spectrum

is the
fundamental

probe
to test
nature of Higgs boson

or to find
alternative EWSB
mechanism

L
SB
<1TeV

SB sector
weakly
coupled

SB sector strongly coupled

eg
,
strongly
interacting light Higgs

SM
No
-
Higgs

L
SB
>1TeV

Unitarity

violation

other scenarios possible:

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

6

Higgs production and decay

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

7

CMS results



WW→lnqq, ZZ→llqq

limited by huge
V+jets background
, taken from simu/data
with large theoretical/statistical error



ZZ→llnn
:



WW→lnln

at high mass limited by signal <<
WW background

(
D

not effective)



>400 GeV limited by
Z+jets

tail at high MET
: not large but not well
known (controlled with
g
+jets

→ statistical
error+met

uncertainty)



200
-
400 GeV limited by
non
-
Z background

(top,
W+jets
, WW)



ZZ→4l

limited by statistics

(only ZZ background: small and well known)

drives the UL for
mH
>
300
-
400

drives the UL for mH 200
-
300

Future
improvements
?



Combination of
>5 different channels

(
ele
, mu,
btag
, …) Robust!



Very optimized analyses
, some space for further improvement. With higher lumi:



use shape analyses (where not yet done)



extract background (norm and shape) from data with lower uncertainty



extract signal with multidimensional fit (now only mZZ fit)

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

9

What’s next ?

higher mass

lower xsec

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

10

1 TeV masses: not anymore “the” Higgs


General search for X→VV→4f:

→ importance of
semileptonic final states

xsec larger than
Higgs:



at high mass still very low
number of events per fb
-
1

RS Graviton vs SM Higgs:

exotic models
(
eg
, Technicolor,

ExtraDimension, …)

first, repeat “Higgs” search for
different spin, width resonance

CMS AN
-
2010
-
35:

Angular
Analysis of Resonances pp → X → ZZ

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

11

Available results: ZZ

low
statistics

MET control V+jets

ZZ→4l

ZZ→llnn



CDF search for G→ZZ
: same features discussed for high mass Higgs @ LHC

ZZ→lljj
: large V+jets

arXiv:1111.3432v1

Available results: W+2jets

CDF “bump”

ATLAS & D0
xchecks

S.Bolognesi (Johns Hopkins University)

13

Control of
V+jets



Improving
theoretical
tools

(
Blackhat
,
Madgraph
, …)



Control region

(
eg
,
Z→jj

sidebands) has very low stat for M(lljj)
~1
TeV



rely on them to extrapolate
at higher energy/multiplicity



test them where we have statistics

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

14



QCD measurement

(jet
p
T
>20
-
30 GeV):

→ syst. dominated by jet
scale, PileUp removal

V+
jets



Data unfolded for detector effects → compared to
NLO
(

hadron

level”)

ATLAS:

February 2012, DESY seminar

15

V+jets

at
Tevatron

At
low
p
T
, low multiplicity:

but
results limited by
systematics

interesting discrepancy data
-
NLO
observed

→ new
variables

D0
novel measurement:
angular
correlations
have
much lower
systematics

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

16

High mass: what’s new ?



Can we simply keep the same Higgs analysis strategy? Not at very high masses!



New experimental issues at very high mass (1 TeV and above)

X → boosted VV →
jet merging (and nearby leptons)



Unknown signal and very small background → no point in pushed optimization! Keep
model independent approach

as much as possible



How to disentangle the various models?



peak → mass and width, xsec and BR



spin
! →
angular analysis

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

17

>1 TeV M(ZZ)→4f : jet merging (1)



Jet merging:

D
R 0.8 (CA) → M
X
>600 GeV

D
R 0.5 (
Akt
) → M
X
>900 GeV

approx

Handles to
distinguish
wrt

to jets from QCD (
eg
, X→ZZ→2l2j VS
Z+jets
):



jet mass

ttbar → WW→ln (jj)

CMS EXO
-
11
-
006

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

18



jet radiation
:

soft/collinear singularity in QCD

no singularity, just decay!

Jet merging (2)

by David
Krohn

(Harvard)

JHU seminar:
Path
-
Integral Jets

www.pha.jhu.edu/groups/particle
-
theory/seminars/talks/F11/talk.khron.pdf

Handles to
distinguish
wrt

to jets from QCD (
eg
, X→ZZ→2l2j VS
Z+jets
):

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

19

Jet pruning



Remove all parts of the jet which are

soft and wide angle

Boosted objects mass reconstruction
improved



QCD jets mass substantially
decreased

-
> lower backgrounds

Typically used for boosted top or
boosted H→bb …

arXiv:0912.0033v1

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

20

Example in X→ZZ→2l2j

First look at Z boosted (no numbers yet) …



M
G

1500 GeV



RS Graviton



CA 0.8

preliminary, A.Bonato, R.Covarelli

X
-
>ZZ
-
>2l2q signal

Z+jets

before jet pruning

after jet pruning

before jet pruning

after jet pruning

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

21

Angular analysis
(1)



X→ZZ→4f
decay kinematic fully defined by 5 angles

signal (M
X

250):

MC from Johns Hopkins

0+

,
0
-

1+

,
1
-

2+m

,
2+L

,
2
-

X→ZZ

Z decays

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

22



Can be clearly used to disentangle different
signals… but
what about background?



Already used in
H→ZZ→2l2q: cut on likelihood



Z+jets from MC: no correlations,



To optimize further (
multidimensional fit
), need full theoretical description of
background:



qq → ZZ:



gg also available → can be used to disentangle qq
-
gg!!



signal: ideal
×

uncorr. accept

(background from jj sidebands)

Angular analysis
(2)

CMS PAS
-
11
-

017

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

23

What’s next ?

higher mass

lower xsec

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

24

Improve

sensitivity



Improve theoretical control of



signal
: →
NNLO&NNLL

effects, precise
mass shape

prediction,
signal
-
background interference
(back
-
up)



background: →

control of
ZZ, WW
ewk

continuum



Factor

5
in luminosity

wrt

to present results



WHY? Models with lower xsec



HOW?

Ex of
(light) composite
higgs
:

(studied in the Higgs Xsec WG and documented in 2 Yellow Report)

First LHC to
Terascale

Workshop (Sept 2011):

LCH at LHC

by J.R. Espinoza

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

25

Diboson

production (WW,WZ,ZZ)



SM test: TGC

fixed by ewk gauge structure

→ any deviation from SM in VV xsec is direct hint of NP in
bosonic

sector



Backgrounds for
high mass Higgs→VV

gg→ VV

(LHC: few % of
xsec with
~
50%
uncertainty)

qqbar

→ VV

WW,WZ,ZZ

forbidden for ZZ

+ NLO qqbar +

forbidden for ZW

TGC

LHC focused on
leptonic

final state,
Tevatron

looked at
semileptonic

but
limited by
systematics

(
V+jets
)

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

26

VV: theoretical
prediction

qq→ZZ NLO + gg→ZZ



Uncertainty dominated by QCD part

February 2012, DESY seminar

27

PDF+
a
s

scale



WW
in
jet
bins
: uncertainty
on
s

㸽丩‫N
浯摥li湧㨠䵃䁎M传


䅌假䕎A





ZZ→
4l: measurement



4l is 0.5% of

ZZ xsec
but
very clean


observed events: 8

expected events: 12.5
±
1.1

Dedicated EWK analysis with very low luminosity, Higgs results much beyond that

39%

16%

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

28

WW
-
>
lnln
: measurement

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

29



Dedicated EWK results only with very low luminosity,



Higgs analysis much beyond that:

stat. and syst. errors
included

37%



First
search for a VBF resonance, feasible in 2012



Measurement of
VV scattering spectrum with
higher
lumi

(>50 fb
-
1
)

From VBF to VV scattering

Typical signature: forward
-
backward
“spectator” jets with very high energy

JHEP 0704 (2007) 052

VBF

ggH

+ 2jets

VBF

ggH

+ 2jets

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

30

Higgs
-
like resonance in VBF



Today only WW→lnln.
Expectations for next year
:



lumi
> 10 fb
-
1



s
⡶(f⤠
縠〮1
×
s
(gg)



0.5 effic. VBF cuts

VBF

yields
in 2012 ~

0.5
gg

yields of 2011
summer results,



ZZ→4l will be still limited by statistics



WW→lnln

will improve S/B (signal/10,
WW*
a
s
2
)



semileptonic final states
will have

reasonable signal yields + much lower
background

than inclusive analysis

eg
,
ZZ→lljj

:



signal yields for
m
H

300
-
500 ~
15


5 events



V+(N+1)jets/V+N jets ~ 0.15 → asking 2 jets
reduces
background to
2
%
!



S/B may increase of

a
factor 2 (
eff

0.5
×

s

〮ㄠ⼠〮〲




RE
-
DO all the analyses in VBF
mode

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

31

with much less background:

summer2011

VV
scattering spectrum



In no Higgs case:

BUT increasing
of xsec at
high VV is suppressed
by

→ small

difference
btw SM and violation of
unitarity

(no Higgs)

→ with proper cut
(
eg

Dh

橥瑳⤠慮a扥
敮桡h敤
-

獥l散瑩潮潦⁴桥l潮i瑵摩湡氠

卉䱈

W
±
W
±

scattering



PDF



offshell

bosons



unpolarized

bosons

reducible background

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

32

Longitudinal polarization

ud
-
>
udWW
-
>
udcs


ud
-
>
udWW
-
>
udcs


mH

500 GeV

noHiggs

(
unitarity

violation)

WW tail (TT): neutrino

WW tail (TT): lepton

Higgs peak (LL): neutrino

Higgs peak (LL): lepton

Transverse distribution

Longitudinal distribution



Angular analysis can boost LL
-
TT separation
(new!):

partonic

study in the
center of mass of W

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

33

VV scattering: interference effects

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

34

...

2

signal

irreducible

background (
a
EW
6
)

qq
-
>6f

O(
a
EW
6
)

WW approximated
without interference



Big interference effects considered only in
Phantom

JHEP 0603 (2006) 093

Accomando
,
Ballestrero
,
Bolognesi
,
Maina
,
Mariotti

=

WW signal with “a
posteriori” cuts

Summary



control
of
V+
jets

(jet pruning)



control uncertainties on
VV EWK continuum

angular analysis



Ingredients along the EWSB road:



search for
VBF

resonance
and
measuring of
VV scattering
spectrum



search for
generic resonance
X
-
>ZZ
-
>4f



Main steps:



The first aim of the Higgs search is
the understanding of the EWSB

-
> focus on H
-
>
VV final state

February 2012, DESY seminar

S.Bolognesi (Johns Hopkins University)

35

BACK
-
UP

18
th

January 2012

Seminar at Johns Hopkins University



S.Bolognesi (Johns Hopkins University)

The road to the ElectroWeak
Symmetry Breaking

Sources

First LHC to Terascale Workshop (Sept 2011):

LCH at LHC

by J.R. Espinoza

CMS AN
-
2010
-
35:
Angular Analysis of Resonances pp → X → ZZ

by David Krohn (Harvard)

JHU seminar:
Path
-
Integral Jets

www.pha.jhu.edu/groups/particle
-
theory/seminars/talks/F11/talk.khron.pdf

Boson Boson scattering analysis

by
A.Ballestrero

(INFN Torino)

LHC To Terascale Physics WS

S.Bolognesi (Johns Hopkins University)

37

Mass shape

From Passarino talk at last LHC to Terascale WS



Present approx:



xsec for
on
-
shell
Higgs
production and decay in
zero width

approx



acceptance from MC with
ad
-
hoc BW distribution

10
-
30% uncertainty on xsec

for
mH

400

600 GeV

Study with QFT
-
consistent Higgs
propagator in the YR2

Higgs qT

q
T

> mH NNLO

q
T

<< mH NNLL

(resumming
ln(mH
2
/q
T
2
))



HqT:

Uncertainties:



factor/renorm scale



PDF



large mt approximation



non perturb. effects

(smearing with NP form factor)

LHC To Terascale Physics WS

S.Bolognesi (Johns Hopkins University)

39

Reweight to HqT



Very small effect on acceptance in 4l: 1
-
2%



HqT used to reweight full event generators (POWHEG at NLO)

mH

120 GeV

mH

500 GeV

H p
T

H y

mH

120 GeV

mH

500 GeV

Powheg

Powheg re
-
weighted to
Hqt

HNNLO

(larger if jet veto!)

LHC To Terascale Physics WS

S.Bolognesi (Johns Hopkins University)

40

(to be redone
before PS)

Signal: jet counting



Analysis in exclusive jet bins

(ex, WW+0,1,2 jets)



if background depends on Njets



for VBF

→ theoretical uncert in jet bins to be
combined with correlations



varying renormalization and
factorization scales in the
fixed
-
order predictions for each exclusive
jet cross section σN

(results as 100% correlated)

different treatments of
the uncontrolled higher
-
order O(α
3
s) terms

i.e., different NNLO
expansions



inclusive xsec (
σ≥Njets
), as source
of
perturbative

uncertainties

σN = σ≥N − σ≥N+1

with error propagation

LHC To Terascale Physics WS

S.Bolognesi (Johns Hopkins University)

41

Signal: jet veto



Resummation of jet
-
veto logarithms

( ln(p
cut
/mH) ), induced by jet cut parameter p
cut

direct exclusive
prediction

from inclusive to
exclusive prediction

LHC To Terascale Physics WS

S.Bolognesi (Johns Hopkins University)

42

Presently doable only on beam thrust variable

(
~raw approx of p
cut
)

and used to reweight MC@NLO

Signal
-
background interference



Recent results for WW, but focused on low mass

Effect on gg→H→WW at LO

m
T

< mH

( arXiv:1107.5569v1 )

non
-
resonant diagrams can be
large for m
T

> mH



Worth to investigate further at high mass?

also shape effects!

01/18/2012 seminar

S.Bolognesi (Johns Hopkins University)

43

ZZ: theoretical
prediction

Single resonant contribution

qq→ZZ NLO + gg→ZZ



ZZ fully from MC, well under control

Interference in the final state with
identical leptons

01/18/2012 seminar

S.Bolognesi (Johns Hopkins University)

44

ZZ: theoretical
uncertainties

PDF+
a
s

scale

qq

gg

qq

gg

01/18/2012 seminar

S.Bolognesi

(Johns Hopkins University)

45

WW: theoretical
uncertainties



WW taken from MC for large
m
H

→ gg+qq NLO available (MCFM)



WW from control region for
m
H
<
200 GeV (
mll
,
D





in jet bins using uncert on
s
㸽丩‫潤敬e湧㨠䵃䁎M传v猠䅌假䕎A

PDF+
a
s

and scale uncertainty

dominates

01/18/2012 seminar

S.Bolognesi (Johns Hopkins University)

46

WW→l

l


measurement

Background

Cuts



Complex analysis (no mass
peak→
counting

experiment, many backgrounds
)



background estimate:



signal acceptance:

leptonic efficiency

jet
-
veto efficiency

missing E
T

uncertainty

theoretical (gg box, PDF)

W+jets

tight lepton quality

top

(b
-
)jet veto

Drell
-
Yan

Z mass veto

missing E
T


WZ, ZZ, W
g

㈠2数t潮

敳瑩浡t敤
from data

→ estimated from MC

01/18/2012 seminar

S.Bolognesi (Johns Hopkins University)

47



Main
systematics
:

WW/WZ→l

2j at CDF



First observation: 5.4
s

⡦(s琠e癩摥v攠a琠䐰睩瑨t㐮4
s

in 2008)



Much
larger backgrounds
, no

resolution

to distinguish W/Z→jj

fit to Mjj (3.9 fb
-
1)

+ matrix element method: (2.7 fb
-
1)



discriminant

exploiting full kinematic
information, based on calculations of differential
xsec of signal and background

QCD from data



data
-
MC validation of input kinematic
variables



fit to shape of discriminant

(NLO expected )

Sara Bolognesi (CERN)

Physics in Collisions, August 2011

48

WZ/ZZ→l
/
2b at Tevatron



WZ → l

ďď н  ї

bb

b
-
tag jets + missing E
T

(+ topological cuts)



Crucial for Higgs search (ZH→

bb). Very complex analysis!



No leptons! → huge background: multijets QCD, V+jets (from data)



very sophisticated techniques:

b
-
tag probability with Boosted Decision Tree or Neural
Network which exploits much info and different variables

different channels combined (0,1,2 b
-
tag)

CDF (2b
-
tags)

D0:

CDF:

(expected 4.6 pb)

(expected 5.1 pb)

Sara Bolognesi (CERN)

Physics in Collisions, August 2011

49



ZZ→2l2


(5.9 fb
-
1)

Shape analysis with fit to neural network

ZZ at CDF



ZZ→4l

(6 fb
-
1) excess of events at high
M
ZZ

(eg Randall Sundrum Graviton)



But xsec still compatible with SM



No excess in other final states



ZZ→2l2j

Control of
Z+jets

very
challenging to
measure ZZ xsec

control of
Z+jets is crucial

Sara Bolognesi (CERN)

50

(NLO expected )

WZ→3l+


at LHC



Very clean, low background

(NLO expected )

CMS:

ATLAS:

Sara Bolognesi (CERN)

Physics in Collisions, August 2011

51

(NLO expected )

Recent WZ→3l+


at Tevatron



D0 with 4.1 fb
-
1



Possible
only at hadron colliders
(charged final state)

statistics 2 times smaller than LHC,
while xsec is 6 times smaller

Shape analysis with fit to neural
network

(NLO expected )



CDF with 7.1 fb
-
1

Sara Bolognesi (CERN)

Physics in Collisions, August 2011

52

observed events: 34

expected signal: 23.3
±
1.5

expected background:



6.0
±
0.6

V+jets
: ratios



Very well known theoretically →
any
deviation is hint of NP



Use high statistics W sample to
predict Z+jets background for NP

CMS PAS EWK
-
10
-
011



Many
systematics

cancel out

01/18/2012 seminar

S.Bolognesi (Johns Hopkins University)

53

The input: signal description



Higgs
p
T

reweighted at NNLO+NNLL
(
Powheg+HqT+HNNLO
)

u
ncertainties
:



factor/
renorm

scale



non perturb.
effects, PDF



Mass shape uncertainty at high mass:



xsec for
on
-
shell
Higgs production and
decay in
zero width

approx



acceptance from MC with
ad
-
hoc BW
distribution

10
-
30% uncertainty on
xsec

for
mH

400

600
GeV

Now shape from proper (QFT
-
consistent)
Higgs propagator available!

Common effort CMS
-
ATLAS
-
theoreticians:
Higgs Xsec working group

(2 yellow reports published:
arXiv:1101.0593 [
hep
-
ph
]

6 Febr. 2012


CERN Winter school

8

S.Bolognesi

(Johns Hopkins University)

arXiv:1201.3084 [
hep
-
ph
]

)

The input: object reconstruction



Leptons (
e,

) from V
:
p
T
>20
GeV
, isolated,
if from Z then M(ll)~91
GeV




Jets:


ATLAS: clusters of calorimeter deposits,
p
T
>25
GeV

CMS: particle
-
flow (full particle identification
with
tracker+calo
),
p
T
>30
GeV



B
-
tagging



MET :

calorimeter deposits (in CMS also part. flow)


-
> optimal performances,
see previous lecturer

6 Febr. 2012


CERN Winter school

9

S.Bolognesi

(Johns Hopkins University)

H
-
>ZZ
-
>ll




2 leptons from Z + MET.



Z+jets


high
D
(jet
-
MET, Z
-
MET)



ttbar



VV mainly irreducible



W+jets

with lepton
fake or from HF



Final cuts:



high MET



high
D
(ll
) or
p
T
Z

-
>
for high
mH



UL from fit to
m
T



Backgrounds:

removed asking for
high, “real” MET

removed vetoing
b
-
tag jets

broad distribution
but pretty good S/B

6 Febr. 2012


CERN Winter school

10

H
-
>ZZ
-
>ll

:
Z+jets

control



Z+jets

is 10
5
×

signal and steeply falling
with MET and
p
T
Z



high MET tail dominated by
fake MET
(difficult to simulate)



cut on
Z boost depends on
Z+jets

modeling

CMS: fully data
-
driven

g
+jets

reweighted
vs


N jets, boson
p
T
, N vertices

boson mass by sampling Z line
-
shape from
fit to data

Main
systematics
:
contamination from

g

+ real MET



Z+jets

left float btw

0 and
g
+jet

prediction

(
-
100%,+0% uncertainty)

ATLAS

MET shape comparison
pythia
-
alpgen

(5
-
20%)

JES

systematics

on MET

7% uncertainty

normalization data
-
MC
comparison
m(ll
) (2.5%)

6 Febr. 2012


CERN Winter school

11

S.Bolognesi

(Johns Hopkins University)

H
-
>ZZ
-
>ll

: non resonant backgrounds



W+jets

normalization from
control region
(same
-
sign
ll

+ MET)



systematics

btag
eff

and
mistag

rate



VV from MC
-
>
systematics

on norm from PDF, scale, missing VZ*



non resonant from data
:



ttbar

from MC



xcheck

in control regions


(
mll

sidebands,
e+mu
)

-
> 9% uncertainty

-
> 100% uncertainty

e+mu

and
m(ll
) sidebands

=

×

-
> 15
-
100% uncertainty



ATLAS:



CMS:

-
> 5
-
10% uncertainty

systematics

from statistics in
e+mu

data

CMS 4.6 fb
-
1

6 Febr. 2012


CERN Winter school

12

S.Bolognesi

(Johns Hopkins University)

H
-
>ZZ
-
>ll

: results

ATLAS includes H
-
>WW
-
>l

l


(13%
-
77%) and H
-
>ZZ
-
>4l, H
-
>ZZ
-
>2l2q

(exclusive cuts
wrt

to dedicated analysis to avoid double counting in combination)

270
-
440
GeV

excluded

310
-
470
GeV

excluded

6 Febr. 2012


CERN Winter school

13

S.Bolognesi

(Johns Hopkins University)

H
-
>ZZ
-
>lljj



2l from Z + 2jets from Z

(to improve
mH

resolution:

kinematic fit M(Z
-
>
jj
) in CMS,

mZ/mjj

rescaling in ATLAS)



Main background
Z+jets



(CMS remove jet from gluons
with
qg
-
likelihhod

discriminant
)



In
2 btag
ttbar

relevant
-
> MET cut
(MET significance in CMS)



no
b
-
jets
-
>
b

categories
(CMS:0,1,2
bjet
; ATLAS: 2
bjets

or
less)



still peaking ~M
Z

because of
kinematic
pT

cuts

6 Febr. 2012


CERN Winter school

14

H
-
>ZZ
-
>lljj: final cuts



ATLAS
: higher
p
T

jets + small
D
(jj
),
D
(ll
)
-
>
high Z
p
T

for high mass Higgs



CMS
: exploit
full angular info
H(spin0)
-
> ZZ
-
>4f
:



UL from
fit to
m(lljj
)

-
>no
m(jj
) bias
-
> background from sidebands

likelihood
discriminant

built with
angles distributions

6 Febr. 2012


CERN Winter school

15

H
-
>ZZ
-
>lljj: background control



shape and normalization
from data
M(jj
) sidebands



Z+jets




shape from MC
-
> uncertainty from
Pythia
-
Alpgen

comparison



All background at once, data
-
driven

(highly dominated by
Z+jets
)



normalization from data
M(jj
) sidebands

-
> uncertainty from data statistics: 1
-
12%
depend. on
mH

and untagged (16%)



ttbar

from MC



xcheck

in MET>50
GeV
,
M(ll
) sidebands

-
> uncertainty from data statistics +
theoretical uncertainty (~15
-
20%)

-
> uncertainty from statistics



rescaled SB/SR from MC

6 Febr. 2012


CERN Winter school

16

S.Bolognesi

(Johns Hopkins University)



ATLAS:



CMS:

Combined results: high mass

127
-
600
GeV

95% CL exclusion

131
-
237 251
-
468
GeV

95% CL exclusion

6 Febr. 2012


CERN Winter school

24

S.Bolognesi

(Johns Hopkins University)